The present invention relates to display devices with low power consumption. In particular, the present invention relates to display devices using liquid crystal elements, EL elements or plasma.
In small-sized liquid crystal displays used in mobile phones or the like, it is important to hold down the power consumption to a small value. In a system proposed in JP-A-2003-5727, therefore, it is attempted to reduce power consumption by displaying only a part of the liquid crystal display and preventing other parts from being displayed at the time of waiting. Hereafter, such a system in which only a part of the display is displayed is referred to as partial display. In JP-A-2003-5727, the drive frequency per frame is lowered and the power consumption is lowered by dividing scanning of the non-display parts into several frames.
On the other hand, TFTs (Thin Film Transistors) are typically used in the small-sized liquid crystal displays currently used in mobile phones. As a conventional TFT material, amorphous silicon is used. Although amorphous silicon has a merit that the manufacturing cost is low, its electron mobility is slow. Therefore, an external LSI is used for the liquid crystal drive circuit. In recent years, LTPS (Low Temperature Poly Silicon) having great electron mobility has been developed, and it has become possible to take the drive circuit and so on into a liquid crystal panel. In a system proposed in U.S. Pat. No. 6,801,194 (JP-A-2002-215118), therefore, the number of components is reduced and the cost is reduced by taking a scanning line drive circuit into the liquid crystal panel.
Furthermore, in a system proposed in JP-A-2003-255904, signals supplied to liquid crystal elements of three colors RGB (Red, Green and Blue) are input to the liquid crystal panel in a time division manner and the cost is reduced by thus reducing the number of connection wires. Hereafter, this system is referred to as RGB time division drive.
By introducing this RGB time division drive, however, an RGB distribution switch for distributing a signal supplied from one signal line in a liquid crystal panel to signal lines connected to liquid crystal elements respectively of R, G and B becomes necessary. Since this RGB distribution switch is operated in a horizontal period, power consumption is high. Therefore, even the partial display for reducing the power consumption has a problem that power consumption in the LTPS-TFT liquid crystal panel in which the RGB time division drive is adopted becomes greater than in the amorphous silicon TFT liquid crystal panel in which the RGB time division drive is not adopted.
In a technique proposed in JP-A-2003-029715 to solve the problem, power consumption is reduced in the partial display by turning on all RGB distribution switches when a signal is input to the non-display part and eliminating variations among control signals to the RGB distribution switches.
Furthermore, introduction of the RGB time division drive poses a problem that the electric charge quantities leaked from respective signal lines become uneven and flicker is generated. In a technique proposed in U.S. Patent Publication No. 2005/156862 (JP-A-2005-195703) to solve this problem, application order of the display signal voltage to respective signal lines is inverted every horizontal period.
Furthermore, in a system proposed in U.S. Patent Publication No. 2003/179335 (JP-A-2003-222891), an equalizer circuit is provided to improve the voltage writing efficiency on the drain signal line and reduce the power dissipation caused by reduction in the driver output load.